Electric heater for thermal treatment furnace

ABSTRACT

A heating element ( 12 ) made of metal wire is installed at an internal circumferential surface of a cylindrical main thermal insulation body ( 11 ) of an electric heater according to the present invention. The heating element ( 12 ) comprises a plurality of resistance heat emitting portions ( 61 )–( 64 ) ( 71 )–( 74 ) ( 81 )–( 84 ) as segments along its length direction. The resistance heat emitting portions ( 61 )–( 64 ) ( 71 )–( 74 ) ( 81 )–( 84 ) are connected in parallel.

BACKGROUND ART

The present invention relates to an electric heater for heat treatingfurnaces, and, particularly, it is suitably used for heat treatingequipments to perform, for example, heat treatments such as oxidation,diffusion, and/or CVD of semiconductor wafers.

Conventionally, an electric heater is known which uses a heating elementinstalled at an internal circumferential surface of its cylindricallyshaped main thermal insulation body, the heating element being formed tocoil shape out of a metal wire referred to as “heavy gauge” whosediameter is 7 to 10 mm.

Then, as a replacement to the above-mentioned electric heater, thepresent applicant proposed previously an electric heater which isdisclosed by a Japanese Patent Application Publication Number2001-267261. This utilizes a metal wire referred to as “light gauge” ofwhich diameter is 1 to 3 mm, and a plurality of parallel grooves areformed at an internal circumferential surface of its main thermalinsulation body extending along its length direction at an interval inits circumferential direction. And a heating element which is made outof a continuous matal wire and formed to sinuous shape with an amplitudebigger than width of the groove is supported unitedly by the mainthermal insulation body with both end portions of its amplitude plungingbeyond the sidewalls of each corresponding groove into the main thermalinsulation body, and meanders in the circumferential direction of themain thermal insulation body so as to extend over all grooves from oneto next.

Because a heavy gauge metal wire is used in the aforementionedconventional electric heater, weight of the heating element is heavy,then, it has a large heat capacity. A problem with such a heater is thata fast heat-up or cool-down cannot be achieved. Besides, energy loss perheat cycle is large.

In this regard, the above-mentioned electric heater of the applicant hassolved these problems by utilizing a light gauge metal wire.

However, since there is a difference in current specification betweenthe former and the latter types of heater, the latter type heater cannotbe employed directly to an existing heat treating equipment where theformer type heaters have been installed. This is because wire diameteris different between both types, then, in order that both types ofelectric heater have an equal output, the latter has to be driven undera high voltage and small current condition, while the former under a lowvoltage and large current condition. For example, a step-downtransformer is required for a low voltage and large current drive, whiletransformer-less usage is presupposed for a high voltage and smallcurrent drive.

Difference in power supply specifications between two types ofconventional heater was mentioned above. Then, to enable an utilizationof a light gauge electric heater with improved thermal characteristicsto replace an existing heat treating equipment where a heavy gaugeheater has been used, compatibility in physical or constitutional aspectis also required in addition to its adaptation to power supplyspecifications. In other words, compatibility related to such as outsidediameter, inside diameter, and length of the heater is required, andfurther, compatibility related to such as division of temperature zonesand its power allotment is required to achieve a temperature profile.

Purpose of the present invention is to provide an electric heater whichcan heat-up and cool-down at a high rate, and moreover, can be driven ata low voltage and large current.

DISCLOSURE OF THE INVENTION

An electric heater for a heat treating furnace according to the presentinvention is characterized by an electric heater for a heat treatingfurnace comprising: a heating element which is made using a metal wireand installed at an inside surface of a main thermal insulation body; aninner thermal insulating material layer and an outer thermal insulatingmaterial layer jacketing outside the main thermal insulation body; andthe heating element comprising a plurality of resistance heat emittingportions which are disposed in parallel in the circumferential directionof the main thermal insulation body, wherein: a pair of connectingmembers which are flat in thickness direction of the main thermalinsulating body and extend along the circumferential direction of themain thermal insulating body are positioned between the inner thermalinsulating material layer and the outer thermal insulating materiallayer respectively at a distance corresponding to the span of the heatemitting portion; and ends of the resistance heat emitting portionpierce through the main thermal insulation body and the inner thermalinsulating material, and are connected to a connecting member ofcorresponding side, respectively.

With the electric heater for a heat treating furnace according to thepresent invention of which main thermal insulation body is installed atits inside surface a heating element which is made using a metal wire,since the heating element comprises a plurality of resistance heatemitting portions connected in parallel, the resistance value of theheating element is lower than that of a heating element made of acontinuous metal wire. Although the heating element uses a light gaugemetal wire, it can be driven under low voltage and large currentcondition which is equivalent to that of the heating element using acontinuous heavy gauge metal wire. In addition, weight of the wire canbe reduced to as small as about 1/10 of that with a heavy gauge wire.Thus, heat capacity of the wire is reduced to about 1/10. This allowsone to provide a heater which can heat-up and cool-down at a high rate,and moreover, can be driven at a low voltage and large current.

Besides, because a pair of connecting members are made to interposebetween the plural resistance heat emitting portions, the resistanceheat emitting portions need not be connected directly among each other.

Further, in case where an inner thermal insulating material layer and anouter thermal insulating material layer jacket outside the main thermalinsulation body, and where both connecting members are positionedbetween the inner thermal insulating material layer and the outerthermal insulating material layer, then, the connecting members can beisolated from high-temperature section of the heater, therefore,unfavorable influence of the parts of the parallel connections ontemperature profile can be avoided, and their thermal distortion hardlyoccurs as well, which secures a construction with high thermalstability.

Furthermore, in the event where a sleeve or a cap is fitted on each endof respective resistance heat emitting portion and fixed by calkingand/or welding, a number of open holes corresponding to the number ofresistance heat emitting portions are opened in each connecting member,and where a sleeve or a cap is put through an open hole at acorresponding end, the sleeve or the cap and fringe of the open hole arewelded, and where the resistance heat emitting portions, connectingmembers, and sleeves or caps are formed out of a same kind of material,then, the discontinuity of physical property, particularlydiscontinuities of metallurgy and thermal expansion coefficient can beavoided between the resistance heat emitting portion, the connectingmember, and the sleeve or the cap, thus, even higher thermal stabilitycan be achieved.

Additionally, in case where a number of parallel grooves not less thanthe number of the resistance heat emitting portions are formed at theinside surface of the main thermal insulation body, each resistance heatemitting portion is formed to a sinuous shape with an amplitude biggerthan width of the groove, supported unitedly by the main thermalinsulation body with both end portions of the amplitude plunging beyondthe sidewalls of each corresponding groove into the main thermalinsulation body, and extending from one groove over to next one atleast, then, a construction is achievable which enables easy use of alight gauge metal wire for a heating element.

Moreover, when the inner insulating material and the outer insulatingmaterial each comprise a pouch made of heat-resistant cloth whichencloses a great many hollow microspheres of microporous thermalinsulating material, both the inner and the outer thermal insulatingmaterials exhibit extremely high thermal insulating characteristic dueto the function of the hollow microspheres.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an exploded perspective view of an electric heater accordingto the present invention.

FIG. 2 is a transverse cross-sectional view of the electric heater.

FIG. 3 is a fragmentary perspective view of the main thermal insulationbody and a heating element of the electric heater.

FIG. 4 is a development view of a heating element of the electricheater.

FIG. 5 is an enlarged transverse cross-sectional view which shows aconnection condition at one end of the heating element.

FIG. 6 is an enlarged transverse cross-sectional view which shows aconnection condition of a part other than the one shown in FIG. 6.

FIG. 7 is an enlarged cross-sectional view of a part shown in FIG. 5.

FIG. 8 is an enlarged cross-sectional view which shows a modifiedexample of a part shown in FIG. 8.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention is explained in the followingmaking reference to the drawings.

Referring to FIGS. 1 and 2, an electric heater comprises a cylindricalmain thermal insulation body (11), a heating element (12) installed atan internal circumferential surface of the main thermal insulation body(11), layers of inner thermal insulating material (13) and outer thermalinsulating material (14) jacketing thereof intervened by a flexible matas a buffer (22) consisting of ceramic fiber covering the externalcircumferential surface of the main thermal insulation body (11), and ametal shell (15) mantling the contour of the outer thermal insulatingmaterial layer (14).

With reference to FIG. 4, the electric heater is, from left to rightsuccessively, allotted for left zone (L), center zone (C) and right zone(R). In FIG. 1, only the left zone (L) and part of the center zone (C)are shown.

The main thermal insulation body (11) is vacuum formed ceramic fiber,which is heat insulating material. At the internal circumferentialsurface of the main thermal insulation body (11) a plurality of parallelgrooves are formed extending along the length direction of the mainthermal insulation body (11) at an interval in its circumferentialdirection. Concretely, the number of grooves (21) in this embodiment istwenty.

The heating element (12) consists of iron-chromium-aluminum alloy, anduses a light gauge metal wire of which diameter is 1–3 mm, as explainedin the beginning.

Part of how a heating element (12) is installed is shown in FIG. 3. Theheating element (12) is formed to sinuous shape. Amplitude of thesinuous shape heating element (12) is made bigger than width of thegroove (21). The heating element (12) formed to sinuous shape issupported unitedly by the main thermal insulation body (11) with bothend portions of its amplitude plunging beyond the sidewalls of thegrooves into the main thermal insulation body.

In FIG. 3, at the left end of first groove (21) from this side, one endof the heating element (12) pierces through bottom of the groove (21)and is made to protrude out of the main thermal insulation body (11).From this end, the heating element (12) meanders, extends to the rightin the groove (21), and reaches the right end of the groove (21). At theright end of the groove (21), the heating element (12) pierces throughthe ridge (wall) in between and gets into the adjoining groove (21)which is second from this side. From there, then, toward the oppositedirection, it extends to the left in the second groove (21). From theleft end of the second groove (21), it gets into the third groove (21),and extends therein to the right, the same direction as in the firstgroove (21) of this side. In this way, the heating element (12),meandering in the circumferential direction of the main thermalinsulation body (11), moves between grooves (21) next to each othersequentially from the first groove (21) of this side to the fifth groove(21) from this side. The heating element (12), after extending in thefifth groove (21) and reaching its right end, pierces through all thewalls (ridges) between adjacent grooves (21) there from, and returnsback to the right end of the first groove (21) of this side. From theright end of the first groove (21) of this side, the other end of theheating element pierces through bottom of the groove (21), and is madeto protrude out of the main thermal insulation body (11).

The above is an example, and configuration of the heating element (12)may be modified appropriately for optimum design. For example, insteadof piercing through walls (ridges) between adjacent grooves (21), aheating element (12) may be configured so as to lay over them.

The inner thermal insulating material (13) includes two types, longpouch (31) and short pouch (32), each formed in half cylinder shape.Each pair of the long or short half cylinder pouches (31) (32) of thesame type abut at their hems (31 a) (32 a) surrounding the main thermalinsulation body (11) to make a complete long or short cylindrical pouch(31) (32), respectively. The long and short pouches (31) (32) arearranged alternately in this order along the length of the main thermalinsulation body (11) from its left edge, and thus, the whole externalsurface of the main thermal insulation body (11) is surrounded by thelong and short pouches (31) (32). Additionally, respective abuttingposition at hems (31 a) (32 a) of adjacent long and short half cylinderpouches (31) (32) is shifted between each other along thecircumferential direction of the main thermal insulation body (11).

The long and short pouches (31) (32) respectively encloses hollowmicrospheres of microporous thermal insulating material in aheat-resistant cladding-material made of silica or glass fabrics, and iscompressed, for example, to form half cylinder shape. It is hardlyflexible, and not easy to deform. Each hollow microsphere is ofmicron-order size containing silica as main constituent, and accumulatesto include a large number of micropores. Silica fabrics ascladding-material are resistant to temperatures higher than 600 degreesCelsius. Inside diameter of a hollow microsphere is made to be less thanmean free path of the atmospheric gas molecules. Therefore, it isunderstood that the atmospheric gas molecules are isolated by walls ofhollow microspheres, and that the probability of a gas molecule beingbounced by the wall becomes so high that collision between gas moleculesis suppressed. Consequently, both the long and short pouches (31) (32)show a superior thermal insulating characteristic.

Although the outer thermal insulating material (14) differs from theinner thermal insulating material (13) in diameter etc., it consists ofboth long and short pouches (31′) (32′) in the same manner as thelatter. These long and short pouches (31′) (32′) are arranged in thesame way as the long and short pouches (31) (32) of the inner thermalinsulating material (13), yet surrounding the entire outside surface ofthe inner thermal insulating material (13). However, arranging order oflong and short pouches (31) (32) (31′) (32′) along the length of themain thermal insulation body (11) is opposite between the inner thermalinsulating material (13) and the outer thermal insulating material (14),and thus, the positions where the facing edges (31 b) (32 b) (31 b′) (32b′) of the neighboring cylindrical long and short pouches (31) (32)(31′) (32′) meet are shifted along the length of the main thermalinsulation body (11). Additionally, two slits (32 c) (32 d) are openedin the short pouch (32′) of the left end of the outer thermal insulatingmaterial (14).

The shell (15) is made of a plurality of stainless steel sheets (41)formed in half cylinder shape. The two shell sheets (41) abut their hems(41 a) each other in similar way as two pouches (31) (32) (31′) (32′),and cover the outer thermal insulating material (14). In one of theshell sheet (41) of the left end are opened slits (41 c) (41 d)corresponding to slits (32 c) (32 d) of the short pouch (32′).

Again, referring to FIG. 4, overall configuration of a heating element(12) is explained in detail. In FIG. 4, the main thermal insulation body(11) is developed in its circumferential direction, and the heatingelement (12) as viewed from outside direction of the main thermalinsulation body (11) is represented.

The heating element (12) comprises a group of resistance heat emittingportions for left zone (51L), a group of resistance heat emittingportions for center zone (51C), and a group of resistance heat emittingportions for right zone (51R). These groups of elements (51L) (51C)(51R) are configured such that they are controllable independently eachother as described below.

The group of resistance heat emitting portions for left zone (51L)comprises four resistance heat emitting portions #1 through #4(61)–(64), which are like splitting a heating element (12) along itslength. The #1 through #4 resistance heat emitting portions (61)–(64)usually employ portions having a same electric resistance value, aredisposed in this order from top to bottom in FIG. 4, and connectedelectrically in parallel. The fourth resistance heat emitting portion(64) corresponds to the heating element (12) that was explainedreferring to FIG. 3. The first through third resistance heat emittingportions (61)–(63) are supported by the main thermal insulation body(11) in the same manner as the fourth resistance heat emitting portion(64). The number of grooves (21) of the main thermal insulation body(11) is twenty as noted earlier, and each 5 grooves (21) correspond toeach of #1 through #4 resistance heat emitting portions (61)–(64).

In the same way as the group of resistance heat emitting portions forleft zone (51L), the group of resistance heat emitting portions forcenter zone (51C) comprises #1 through #4 resistance heat emittingportions (71)–(74), and the group of resistance heat emitting portionsfor right zone (51R) includes #1 through #4 resistance heat emittingportions (81)–(84). These resistance heat emitting portions (71)–(74)(81)–(84) are also supported by the main thermal insulation body (11) inthe same manner as the fourth resistance heat emitting portion (64) ofthe group of resistance heat emitting portions for left zone (51L).

At the left side of the group of the resistance heat emitting portionsfor left zone (51L) are disposed two, i.e. upper and lower, firstconnecting members (91) (92) in strip form so as to extend along top tobottom direction. The first upper and lower connecting members (91) (92)are connected by first joint bar (93). Similarly, at the right side ofthe group of the resistance heat emitting portions for left zone (51L)are disposed two, i.e. upper and lower, second connecting members (94)(95) in strip form. The second upper and lower connecting members (94)(95) are connected by second joint bar (96).

In the same way as the group of resistance heat emitting portions forleft zone (51L), the group of resistance heat emitting portions forcenter zone (51C) comprises connecting members (101) (102) (104) (105)and joint bars (103) (106), and the group of resistance heat emittingportions for right zone (51R) includes connecting members (111) (112)(114) (115) and joint bars (113) (116).

The left ends of the first and second resistance heat emitting portions(61) (62) of the group of resistance heat emitting portions for leftzone (51L) are connected to the first upper connecting member (91), andtheir right ends are connected to the second upper connecting member(94). The left ends of the third and fourth resistance heat emittingportions (63) (64) of the same group of resistance heat emittingportions (51L) are connected to the first lower connecting member (92),and their right ends are connected to the second lower connecting member(95). Parallel connections of the group of resistance heat emittingportions for left zone (51L) are realized by the above method. Theembodiment of the connection is similarly applicable to the groups ofresistance heat emitting portions for center zone (51C) and right zone(51R) as well.

To the first lower connecting member (92) to the group of resistanceheat emitting portions for left zone (51L) is connected first terminal(121) of L-shaped strip. To the second upper connecting member (94) tothe group of resistance heat emitting portions for left zone (51L), andto the first upper connecting member (101) to the group of resistanceheat emitting portions for center zone (51C) is connected left middleterminal (122) made of L-shaped strip, extending over both connectingmembers (94) (101). Further, to the second upper connecting member (104)to the group of resistance heat emitting portions for center zone (51C),and to the second upper connecting member (111) to the group ofresistance heat emitting portions for right zone (51R) is connectedright middle terminal (123) made of L-shaped strip, extending over bothconnecting members (104) (111). To the first lower connecting member(115) to the group of resistance heat emitting portions for right zone(51R) is connected second terminal (124) made of L-shaped strip. Thus,the heating element (12) is connected such that the group of resistanceheat emitting portions for left zone (51L), the group of resistance heatemitting portions for center zone (51C), and the group of resistanceheat emitting portions for right zone (51R) are electricallycontrollable independently.

FIG. 5 shows where connections are made between left ends of the firstand second resistance heat emitting portions (61) (62) of the group ofresistance heat emitting portions for left zone (51L) and the firstupper connecting member (91). Over a respective end of the first andsecond resistance heat emitting portions (61) (62) is fitted first andsecond cylindrical sleeves (131) (132), respectively. Each sleeve (131)(132), caulked and then welded, is fixed to the corresponding end of theresistance heat emitting portions (61) (62). The connecting member (91)has a round hall (141) and an oval hole (142). In agreement with theround hall (141) and the oval hole (142), two round holes (143) (144)are opened in the inner thermal insulating material (13). The firstsleeve (131) pierces through the two round holes (141) (143). Theexternal surface of the sleeve (131) is welded to the fringes of theround holes (141) (143). The second sleeve (132) pierces through theoval hole (142) and the round hole (144). The external surface of thesleeve (132) is welded to the fringes of the oval hole (142) and theround hole (144).

An embodiment of the above-mentioned welding of the first sleeve (131)is shown in detail in FIG. 7. A welding aperture (145) is opened throughthe circumferential wall of the first sleeve (131). A weldment (146) isformed so that the welding aperture (145) is full. Further, anotherweldment (147) is formed which jackets the end of the first resistanceheat emitting portion (61), the first sleeve (131) and its perimeter.

FIG. 6 shows where a connection is made with the first lower connectingmember (92) at left end of the third resistance heat emitting portion(63) of the group of resistance heat emitting portions for left zone(51L). Over an end of the third resistance heat emitting portion (63) isfitted a cylindrical sleeve (151) also. An oval hole (162) is formed inthe connecting member (92). A round hole (163) is opened in the innerthermal insulating material (13) in agreement with this oval hole (162).The sleeve (92) pierces through an oval hole (162) and a round hole(163), and is connected to the connecting member (92) by welding.Additionally, FIG. 6 shows the way how the first terminal (121) iswelded to the connecting member (92). Although not explained, anembodiment of the connection of other resistance heat emitting portions(64) (71)–(74) (81)–(84) with connecting members (91) (94) (95) (104)(105) (111) (112) (114) (115), and an embodiment of the connection ofthe connecting members (94) (101) (104) (111) (115) with terminals (122)(123) (124) are similar to the above.

FIG. 8 shows an example using a cap (181) instead of a cylindricalsleeve (131) shown in FIG. 7. A welding aperture (182) is opened to thecircumferential wall of the cap (181). The welding aperture (182) isfilled with a weldment (183), and top face of the cap (181) and itsperiphery are covered with another weldment (184).

Moreover, the first and second sleeves (131) (132) pierce through theinner thermal insulating material (13) and are made to protrude to itsoutside, where they are welded to the first upper connecting member(91). The first upper connecting member (91) is put between the innerthermal insulating material (13) and the outer thermal insulatingmaterial (14). Referring to FIG. 6, the sleeve (151), to which isinlayed the third resistance heat emitting portion (63), also piercesthrough the inner thermal insulating material (13) and is made toprotrude to its outside, where it is welded to the first lowerconnecting member (92). Additionally, the first lower connecting member(92) is put between the inner thermal insulating material (13) and theouter thermal insulating material (14). Although not illustrated, otherconnecting members (94) (101) (104) (111) (115) are, likewise, putbetween the inner thermal insulating material (13) and the outer thermalinsulating material (14).

Again, referring to FIG. 1, one can understand that the first terminal(121) is put through the slits (32 d) (41 d) on one side of the outerthermal insulating material (14) and the shell (15), while the leftmiddle terminal (122) is put through slits (32 c) (41 c) on the otherside.

All connecting members (91) (92) (94) (95) (104) (105) (111) (112) (114)(115), joint bars (93) (96) (103) (106) (113) (116), terminals (121)(122) (123) (124), sleeves (131) (132) (151), and a cap (181) consist ofa same material as the heating element (12), namely metal ofiron-chromium-aluminum system. By this configuration, one can overcomethe troublesome sigma brittleness which is peculiar to this material,namely a property of getting brittle once it is heated to a hightemperature.

As is apparent from the above-mentioned description, the presentinvention is neither limited to a heater of cylindrical shape, nor tosemi-conductor heat treating furnace. For example, it can also beapplied to flat plate type heater, and therefore find many applicationsin engineering fields.

Moreover, the present invention is not limited to what is disclosed inthe above description, and various kinds of modifications are possiblewithout departing from the scope of the present invention.

INDUSTRIAL APPLICABILITY

The electric heater of the present invention is particularly suitablefor use as an electric heater for heat treating furnaces to perform, forexample, heat treating equipments for oxidation, diffusion, and/or CVDof a semiconductor wafer.

1. An electric heater for a heat treating furnace comprising: a heatingelement which is made using a metal wire and installed at an insidesurface of a main thermal insulation body; an inner thermal insulatingmaterial layer and an outer thermal insulating material layer jacketingoutside the main thermal insulation body; and the heating elementcomprising a plurality of resistance heat emitting portions which aredisposed in parallel in the circumferential direction of the mainthermal insulation body, wherein: a pair of connecting members which areflat in thickness direction of the main thermal insulation body andextend along the circumferential direction of the main thermalinsulation body are positioned between a inner thermal insulatingmaterial layer and the outer thermal insulating material layerrespectively at a distance corresponding to a span between the heatemitting portions; and ends of each of the resistance heat emittingportions pierce through the main thermal insulation body and the innerthermal insulating material layer, and are connected to a connectingmember of corresponding side, respectively.
 2. The electric heater for aheat treating furnace according to claim 1, wherein the inner insulatingmaterial and the outer insulating material layers each comprise a pouchmade of a heat-resistant cloth which encloses a great number of hollowmicrospheres of microporous thermal insulating material.
 3. The electricheater for a heat treating furnace according to claim 1, wherein: asleeve is fitted on respective ends of respective resistance heatemitting portions, and fixed by at least either of calking and welding;a number of open holes corresponding to the number of resistance heatemitting portions are opened in respective said connecting members; andthe sleeve is put through an open hole at corresponding end, and thesleeve and fringe of the open hole are welded.
 4. The electric heaterfor a heat treating furnace according to claim 1, wherein: a cap isfitted on respective ends of respective resistance heat emittingportions, and fixed by at least either of calking and welding; a numberof open holes corresponding to the number of resistance heat emittingportions are opened in respective said connecting members; the cap isput through an open hole at corresponding end, and the cap and fringe ofthe open hole are welded; and the resistance heat emitting portions, theconnecting members, and the caps are formed out of a same kind ofmaterial.
 5. The electric heater for a heat treating furnace accordingto claim 1, wherein: a plurality of parallel grooves not less than thenumber of the resistance heat emitting portions are formed on the insidesurface of the main thermal insulation body; each of the resistance heatemitting portions is formed to sinuous shape with an amplitude biggerthan width of the groove, supported unitedly by the main thermalinsulation body with both end portions of the amplitude plunging beyondthe sidewalls of the corresponding groove into the main thermalinsulation body, and extending over to at least one neighboring groove.